Art of radio signaling



Sept. 22, 1936. COHEN 2,055,375

' ART OF RADIO SIGNALING Filed Dec. 13, 1932 INVENTOR.

Patented Sept. 22, 1936 UNITED STATES PATENT OFFICE 13 Claims.

This invention relates to the art of radio signaling. It has for its particular object'providing methods and means for securing constancy of frequency in the oscillations produced by vacuum tube oscillation generators. 3 p 1 It is well known in the art that thefrequency of the oscillations produced by vacuum tube generators depends in some degree on the internal resistance (plate-filament) of the tube, and the resistance of the oscillation circuit. A variation in either of these factors causes a variation in the frequencyof theoscillations, The internal resistance of the tube depends on the plate voltage, and therefore any variation in the voltage supply causes a change in the frequency of the oscillations. Also a variation in the load, that is the resistance of the oscillation circuit causes a variation in the frequency. In the use of vacuum tube oscillators in transmitting stations, it is necessary for eflicient operation, particularly from the standpoint of minimizing interference, to maintain constancy of frequency. The Federal Radio Commission has made stringent regulations in regard to thepermissible deviation from the assigned frequency to a station. f

In the present day practice constancy of frequency of vacuum tube generators is secured through the use of quartz crystal control, which is an effective 'method, but requires additional equipment adding to'the cost of installation, and

to difiiculties in maintenance. It would be of advantage if the constancy of frequency could be maintained without the aid ofcrystals, and it is tothe realization of this objective that this invention is directed. A circuit system is provided in this invention whereby the tendency to frewhich forms part of this specification.

Figure I shows a circuit system in which the a grid circuit is tuned; Figure II is a modification providing for the tuning of the plate circuit; and Figure III shows a modified Hartley circuit.

In thecircuit arrangement shown in Figure I, a tuned circuit consisting of inductance coil l and variable condenser 2 in parallel together with an additional inductance coil 3 in series with the tuned circuit I', '2, are connected in the grid filament circuit 4, 5. =The coils land 3 are'in inductive relation to coils 6 and 1 respectively, the inductance coils 6 and 1 forming part of the plate filament circuit 8, 1, 6, 5. By the adjustment of the mutual inductance between the coils l and 6 a proper degree of regeneration may be 6 established to set up oscillations in the oscillatory circuit l, 2; this is one of the usual methods for exciting oscillations in a vacuum tube circuit by feed-back; The additional transformer 3, 1 provides a means for maintaining the frequency .10 of the oscillations constant, and may be designated as a stabilization transformer. By suitable adjustment of the mutual inductance between coils 3 and I a condition is obtained whereby the frequency of the oscillations is maintained constant independent of any variation in the internal resistance (plate-filament) of the tube,

or any variation in the load, the resistance of the oscillation circuit.

Without limiting myself to any theory of operation I believe the following may be the explanation of the operation of my invention. In vacuum tube oscillators, whatever the type of regeneration circuit, the principal frequency determining elements are the inductance and capacity of the oscillatory circuit and a factor which is a function of ,T is that the circuit containing the plate resistance is either in shunt or in inductive relation to the inductance of the oscillatory circuit, and in either case the effective value of the inductance is modified thereby; To eliminate the influence of the tube resistance on the frequency, it is necessary to provide additional regenerative coupling to compensate for the oscillatory energy dissipation in the tube resistance, and this is accomplished by the circuit arrangements provided in this invention. I

The required mutual inductance between coils -3 and 1 to realize the condition of constant frequency is given by the formula,

the matter of degree of coupling may be determined experimentally. Keeping L1 the induc tance of the plate circuit fixed, it is only a matter of varying M2, the mutual inductance between coils 3 and 1, until the condition of constant :fre-

quency, which is the condition given formula, is obtained.

v Figure II is a modification in which the tuned circuit i2,;l 3 is connected in the plate circuit. The coupling of the plate tuned circuit to the grid by -transformer l0, l2 provides the necessary feed-backto maintain oscillationsin the oscilla- :tory, circuit. The additional coupling of plate and grid circuits throughtransfor-mer 9, ll provides rr eans for frequency: stabilization, that is the-maintenance of constant frequency, counteracting any tendency .to frequency variation resulting from changes in'either the internal reby the .sistance of the tube or in the load. To realize the condition-of frequency stabilization in Figure .11, the following relations must obtain:

and

7 IIl ZILMl, where L2 is the self inductance of coil 12 of the oscillatory circuit; L1 is the self inductance of coil; @is the. amplification factor'of the tube, and M1 is the mutual inductance between coils 9 and II I, The abo'veformulaswere derived from a mathematical analysis. of the problem, and

give the necessary relationship between the various-elements of the',.circuit to obtain the condition of frequency stabilization. The desired condition may be also obtained experimentally without regard to the formulas.

In Figure III a modified Hartley circuit is shown, thenovellfeature consisting in the additional coupling between plate and grid provided by transformer I4, I 5: The transformer 14, I5 provides a means for maintaining the frequency of the oscillations substantially constant. By suitably adjusting the mutual inductance between coils M and l5in relation to theotherelements of th'e circuit system a-condition is obtained Whereby the frequency of the oscillations is maintained substantially constant independent of any variation in the internal resistance (plate-filament) of the tube, orany variation in the load, or the resistance er the oscillation circuit. The value of the mutual inductancebetween [4 and I5 re- "quired depends on the values'of the inductances l6 and H, the mutual inductance between them, and' al'so 'on the self inductance "of transformer coil-I l, but in practice it is merely amatter of adjusting the mutual inductance between the co'ils 'l'4iand I5 to attain-the desired result. lIhe three circuitsshown in the figures illustrate different embodiments of my invention.

. By the practice of the invention disclosed the frequency of "vacuum tube oscillators is rendered substantially invariantiwithrespect-to variations in tube resistance, load, or energizing voltage. The frequency is rendered substantially invariant with respect to Variations in any one or more of these factors. The same principle may be employed in connection with any other type of vacuum tube oscillator to secure constancy of frequency. Many variations in the details of the apparatus and methods disclosed will be apparent to those skilled in the art, and many applications of the invention besides those described will be apparent. I-do not intend therefore to be limited except as required by the prior art and as indicated in the accompanying claims.

Iclaimas my invention:

1'. A vacuum tube oscillation generator having "a.frequency'determining circuit in the grid circuit thereof, an inductance in the plate circuit thereof regeneratively coupled to said frequency determining circuit so as to set up oscillations, and a magnetic coupling betweenthe plate and grid circuits of said oscillation generator of such magnitude that pM2= L1 v where ,u. 'is the amplification factor of the tube, M2 is the mutual inductanceof said coupling, and his the self inductance of the plate circuit, no part of said magnetic coupling being included in the frequency determining circuit.

2. The combination with'a vacuum tube oscillation generator having a frequency determining circuit in the plate circuit thereof and an inductance in the grid circuit thereof regeneratively. coupled to said frequency determining circuit so as to set up oscillations, of frequency stabilizing means comprising an inductance in the plate circuit and an inductance in the grid circuitcoupledthereto, said coupling and said inductance being of such magnitude that where ,u is the amplification factor of the tube, M1 is the mutualinductance of said coupling, and L1 is theself inductance of said plate circuit inductance, the self, inductance of the frequency determining circuit L2 being of such magnitude that where L1 has the same meaning as above, no part of saidsfrequency stabilizing means being ineluded-in the frequency determining circuit.

3. The combinationof aHartley oscillator and frequency stabilizing means common to the plate and grid circuits thereof, said stabilizing means comprising a magnetic coupling between the :plate and. grid circuits of said oscillator, no part of said coupling being included in the. frequency determining circuit of said oscillator.

4. An oscillation generator comprising a tube having an anode, cathode, and grid, a circuit between said anode and cathode and a circuit between said grid and cathode, two inductances in series in each of said circuits, one inductance in eachcircuit beingcoupled to one inductance only in the other circuit, and means for tuning one only of'said'inductances to a desired frequency.

'5. 'An oscillation generator comprising a tube having an anode, cathode and grid, a circuit only of said inductances to a desired frequency,

and'imeans to adjust the mutual inductance of the coupling not involving the tuned inductance to render the frequency substantially invariant with respect to tube resistance and energizing voltage.

6. Vacuum tube oscillation generator comprising a vacuum tube having a cathode, anode and grid, a circuit between the cathode and anode and a circuit between the grid and anode, two in'ductances in series in each of said circuits, each inductance in each circuit being coupled to one inductance only in the other circuit, and means for tuning one inductance in the grid-cathode circuit to a desired frequency.

7. An oscillation generator comprising a vacuum tube having a cathode, anode and grid, a circuit between said anode and cathode and a circuit between said grid and cathode, two inductances in series in each of said circuits, each inductance in each of said circuits being coupled to one inductance only in the other of said circuits, means for tuning one inductance in the grid-cathode circuit to a desired frequency, and means to adjust the mutual inductance between the untuned inductance in the grid-cathode circuit and the inductance in the anode-cathode circuit coupled thereto to render the oscillation frequency substantially invariant with respect to tube resistance and energizing voltage.

8. A vacuum tube oscillation generator comprising a vacuum tube having a cathode, anode and grid, a circuit between said anode and cathode and a circuit between said cathode and grid, two inductances in series in each of said circuits, each inductance in each circuit being coupled to one inductance only in the other circuit, and means for tuning one inductance in the anodecathode circuit to a desired frequency.

9. A device as in claim 8 wherein the tuned inductance is the one further from the anode, the inductance in the anode-cathode circuit nearest the anode being coupled to the inductance in the grid-cathode circuit nearer the grid, the constants of the system being such that where ,u. is the amplification factor of the tube, M1 is the mutual inductance of said last named coupling, L1 is the self inductance of the untuned inductance in the plate-cathode circuit, and L2 is the self inductance of the tuned inductance in the anode-cathode circuit.

10. A vacuum tube oscillation generator comprising a vacuum tube having a cathode, anode and grid, a circuit between said anode and cathode and a circuit between said grid and cathode, two inductances in series in each of said circuits, each inductance in each of said circuits being coupled to one inductance only in the other of said circuits, means for tuning one inductance in the anode-cathode circuit to a desired frequency, and means to adjust the mutual inductance between the untuned inductance in the anode-cathode circuit and the inductance in the grid-cathode circuit coupled thereto to render the oscillation frequency substantially invariant with respect to tube resistance and energizing voltage.

11. -In a Hartley oscillation generator comprising a vacuum tube having a cathode, anode and grid, a circuit between the anode and cathode, a circuit between the grid and cathode, and a frequency determining circuit included in both the grid-cathode and anode-cathode circuits; a frequency stabilizer comprising an inductance in the grid-cathode circuit between the grid and the frequency determining circuit and an inductance in the anode-cathode circuit between the anode and frequency determining circuit coupled to the first mentioned inductance.

12. In a Hartley oscillation generator comprising a vacuum tube having a cathode, anode, and grid, a circuit between the anode and cathode, a circuit between the grid and cathode, and a frequency determining circuit included in both the grid cathode and anode cathode circuits; a frequency stabilizing means comprising an inductance in the grid-cathode circuit between the grid and the frequency determining circuit, an inductance in the anode-cathode circuit between the anode and frequency determining circuit coupled to said first named inductance and means to adjust the mutual inductance between said inductances torender the oscillation substantially invariant with respect to tube resistance and energizing voltage.

13. A Hartley oscillator having a magnetic coupling between the plate and grid circuits of said oscillator, no part of said coupling being included in the frequency determining circuit of said oscillator, and means to vary the mutual inductance of said coupling to render the oscillation frequency substantially invariant with respect to tube resistance, load, and energizing voltage.

LOUIS COHEN. 

